Meltblown web

ABSTRACT

A meltblown fiber comprising at least 20% by weight polyester selected from the group consisting of poly(ethylene terephthalate) having an intrinsic viscosity of less than 0.55 dl/g and poly(trimethylene terephthalate) having an intrinsic viscosity of less than 0.80 dl/g is provided. The meltblown fibers are collected as a web that can be incorporated into composite sheet structures.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to meltblown fibers, meltblown fiber webs,and composite nonwoven fabrics that include meltblown fibers. Themeltblown webs of the invention can be incorporated in composite fabricssuited for use in apparel, wipes, hygiene products, and medical wraps.

[0003] 2. Description of Related Art

[0004] In a meltblowing process, a nonwoven web is formed by extrudingmolten polymer through a die and then attenuating and breaking theresulting filaments with a hot, high-velocity gas stream. This processgenerates short, very fine fibers that can be collected on a moving beltwhere they bond with each other during cooling. Meltblown webs can bemade that exhibit very good barrier properties.

[0005] Meltblown fibers are most typically spun from polypropylene.Other polymers that have been spun as meltblown fibers includepolyethylene, polyamides, polyesters, and polyurethanes. Polyesterpolymers, such as poly(ethylene terephthalate) (“PET”) andpoly(trimethylene terephthalate) (“PTT”), are not well adapted formaking fine meltblown fibers. In addition, due to polyester's low degreeof crystallization when formed in meltblown webs and due to polyester'slow crystallization temperature, thermally bonded meltblown polyesterwebs tend to be brittle and they exhibit relatively poor fluid barrierproperties, especially when subjected to mechanical stress. U.S. Pat.No. 5,364,694 discloses the meltblowing of a blend of PET with anotherthermoplastic polymer, such as polyethylene, which is incompatible withPET and has a high crystallization rate and a low melt viscosity. Thesecond polymer produces a “viscosity-reducing effect” that decreases themelt viscosity of the entire blend, so as to facilitate attenuation ofPET when meltblown. U.S. Pat. No. 4,795,668 discloses the meltblowing ofbicomponent fibers wherein one component is PET and the other componentis a more thermally stable polymer such as polypropylene or polystyrene.

[0006] Meltblown fibers have been incorporated into a variety ofnonwoven fabrics including composite laminates such asspunbond-meltblown-spunbond (“SMS”) composite sheets. In SMS composites,the exterior layers are spunbond fiber layers that contribute strengthto the overall composite, while the core layer is a meltblown fiberlayer that provides barrier properties. Traditionally, the spunbond andmeltblown layers of SMS composites have been made of polypropylenefibers. For certain end use applications, such as medical gowns, it isdesirable that SMS composite sheets have good strength and barrierproperties, while also being as soft and drapeable as possible. Whilepolypropylene-based SMS fabrics offer good strength and barrierproperties, they tend not to be as soft and drapeable as is desirablefor apparel products. Polypropylene-based SMS fabrics also have thelimitation that they cannot be sterilized with gamma radiation becausesuch fabrics are discolored and weakened when sterilized with gammaradiation, and because gamma radiation sterilization ofpolypropylene-based SMS fabrics generates unpleasant odors. A polymerfiber or fabric is generally considered to be not radiation sterilizablewhen sterilization of the fabric with gamma radiation causes asignificant reduction in the strength of the fiber or fabric, noticeablychanges the appearance of the fiber or fabric, or generates anobjectionable odor. This inability to undergo gamma radiationsterilization presents a significant problem for polypropylene-based SMSfabrics because radiation sterilization is commonly used throughout themedical industry.

[0007] There is a need for finer polyester meltblown fibers that whenformed into webs exhibit good barrier properties. There is a furtherneed for meltblown polyester webs that are pliable and do not experiencea significant loss in barrier properties when mechanically stressed.

BRIEF SUMMARY OF THE INVENTION

[0008] The present invention is directed to a meltblown fiber and a webof meltblown fibers. The meltblown fiber of the invention comprises atleast 20% by weight polyester selected from the group consisting ofpoly(ethylene terephthalate) having an intrinsic viscosity of less than0.55 dl/g, and poly(trimethylene terephthalate) having an intrinsicviscosity of less than 0.80 dl/g. The meltblown fiber of the inventionhas an average effective diameter of less than 10 microns. Preferably,the intrinsic viscosity of the poly(ethylene terephthalate) is in therange of 0.20 to 0.50 dl/g and the intrinsic viscosity of thepoly(trimethylene terephthalate) is in the range of 0.45 to 0.75 dl/g.More preferably, the intrinsic viscosity of the poly(ethyleneterephthalate) is in the range of 0.25 to 0.45 dl/g and the intrinsicviscosity of the poly(trimethylene terephthalate) is in the range of0.50 to 0.70 dl/g. Meltblown fibers of the invention are preferablyformed into a meltblown web.

[0009] According to one preferred embodiment of the invention, themeltblown fiber is a multiple component fiber comprised of between 20%and 98% by weight of poly(ethylene terephthalate) and between 80% and 2%by weight of a second polymer component comprised of at least 10% ofpolyethylene polymer. Meltblown fibers of the invention are preferablyformed into a multiple component meltblown web comprised of between 20%and 98% by weight of poly(ethylene terephthalate) and between 80% and 2%by weight of a second polymer component comprised at least 10% by weightof polyethylene polymer.

[0010] The present invention is also directed to a composite sheethaving a first fibrous layer having a first side and an opposite secondside, and a second fibrous layer bonded to the first side of the firstfibrous layer. The first fibrous layer is a meltblown web comprised ofat least 20% by weight polyester selected from the group consisting ofpoly(ethylene terephthalate) having an intrinsic viscosity of less than0.55 dl/g, and poly(trimethylene terephthalate) having an intrinsicviscosity of less than 0.80 dl/g. The second fibrous layer is preferablycomprised of at least 95% by weight of meltspun fibers. In the preferredembodiment of the invention, the composite sheet has a basis weight ofless than 120 g/m², and a hydrostatic head of at least 10 cm. Accordingto a more preferred embodiment of the invention, at least 10% of themeltblown fibers in the first fibrous layer are multiple componentfibers. More preferably the multiple component meltblown fibers have alow intrinsic viscosity polyester component and a polyethylenecomponent. According to the invention, the meltspun fibers of the secondfibrous layer can be multiple component fibers having a polyestercomponent and a polyethylene component. The invention is also directedto garments made of the composite sheet of the invention.

[0011] The present invention is also directed to a meltblown fibercomprising at least 20% by weight polyester having a weight averagemolecular weight of less than 25,000. Preferably, the polyester has aweight average molecular weight in the range of 5,000 to 22,000. Morepreferably, the polyester has a weight average molecular weight in therange of 10,000 to 19,000.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 is a schematic diagram of a portion of an apparatus usedfor producing meltblown fibers for use in the composite nonwoven fabricof the invention.

[0013]FIG. 2 is a diagrammatical cross-sectional view of a compositenonwoven fabric in accordance with one embodiment of the invention.

[0014]FIG. 3 is a diagrammatical cross-sectional view of a compositenonwoven fabric in accordance with another embodiment of the invention.

[0015]FIG. 4 is schematic illustration of an apparatus for producing thecomposite nonwoven fabric of the invention.

DEFINITIONS

[0016] The term “polymer” as used herein, generally includeshomopolymers, copolymers (such as for example, block, graft, random andalternating copolymers), terpolymers, and blends and modificationsthereof. Furthermore, unless otherwise specifically limited, the term“polymer” shall include all possible geometrical configurations of thematerial. These configurations include isotactic, syndiotactic andrandom symmetries.

[0017] The term “polyethylene” as used herein is intended to encompassnot only homopolymers of ethylene, but also copolymers wherein at least85% of the recurring units are ethylene units.

[0018] The term “polypropylene” as used herein is intended to embracenot only homopolymers of propylene but also copolymers wherein at least85% of the recurring units are propylene units.

[0019] The term “polyester” as used herein is intended to embracepolymers wherein at least 85% of the recurring units are condensationproducts of dicarboxylic acids and dihydroxy alcohols with polymerlinkages created

[0020] by formation of an ester unit. This includes aromatic, aliphatic,saturated, and unsaturated di-acids and di-alcohols. The term“polyester” as used herein also includes copolymers (such as block,graft, random and alternating copolymers), blends, and modificationsthereof. A common example of a polyester is poly(ethylene terephthalate)which is a condensation product of ethylene glycol and terephthalicacid.

[0021] The term “meltspun fibers” as used herein means fibers which areformed by extruding molten thermoplastic polymer material as filamentsfrom a plurality of fine, usually circular, capillaries of a spinneretwith the diameter of the extruded filaments then being rapidly reduced.Meltspun fibers are generally continuous and have an average diameter ofgreater than about 5 microns.

[0022] The term “meltblown fibers” as used herein means fibers formed byextruding a molten thermoplastic polymer through a plurality of fine,usually circular, capillaries as molten threads or filaments into a highvelocity gas (e.g. air) stream. The high velocity gas stream attenuatesthe filaments of molten thermoplastic polymer material to reduce theirdiameter to between about 0.5 and 10 microns. Meltblown fibers aregenerally discontinuous fibers. Meltblown fibers carried by the highvelocity gas stream are normally deposited on a collecting surface toform a web of randomly dispersed fibers.

[0023] The term “spunbond fibers” as used herein, means fibers that areformed by extruding molten thermoplastic polymer material as filamentsfrom a plurality of fine capillaries of a spinneret, drawn, randomlydeposited onto a screen and bonded together.

[0024] The term “nonwoven fabric, sheet or web” as used herein means astructure of individual fibers or threads that are positioned in arandom manner to form a planar material without an identifiable pattern,as in a knitted fabric.

[0025] The term “multiple component meltblown web” as used herein meansmeltblown fibers spun from fine capillaries as molten filamentscontaining multiple and distinct polymer components, which moltenfilaments are attenuated by a high velocity gas stream and deposited ona collecting surface as a web of randomly dispersed fibers.

[0026] As used herein, the “machine direction” is the long directionwithin the plane of a sheet, i.e., the direction in which the sheet isproduced. The “cross direction” is the direction within the plane of thesheet that is perpendicular to the machine direction.

Test Methods

[0027] In the description above and in the examples that follow, thefollowing test methods were employed to determine various reportedcharacteristics and properties. ASTM refers to the American Society forTesting and Materials, and AATCC refers to the American Association ofTextile Chemists and Colorists.

[0028] Intrinsic Viscosity (IV) is a measure of the inherent resistanceto flow for a polymer solution and was determined by ASTM D-2857, whichis hereby incorporated by reference, and is reported in dl/g. Thesolvent and temperature used to study the intrinsic viscosity ofpoly(ethylene terephthalate) in a glass capillary viscometer washexafluoropropanol with 0.01 M sodium trifluoroacetate at 35° C. Thesolvent and temperature used to study the intrinsic viscosity ofpoly(trimethylene terephthalate) in a glass capillary viscometer wasorthochlorophenol at 25° C.

[0029] Weight Average Molecular Weight was measured using size exclusionchromatography analysis with a triple detector system. This systemallows an absolute molecular weight to be measured independent of thetype of calibration standards. The molecular weight averages forpoly(ethylene terephthalate) were determined in hexafluoroisopropanolwith 0.01 M sodium trifluoroacetate using an injection volume of 100microliters operating at 1.000 mL/min flow rate at 35 C.

[0030] Fiber Diameter was measured via optical microscopy and isreported as an average value in microns.

[0031] Basis Weight is a measure of the mass per unit area of a fabricor sheet and was determined by ASTM D-3776, which is hereby incorporatedby reference, and is reported in g/m².

[0032] Grab Tensile Strength is a measure of the breaking strength of asheet and was conducted according to ASTM D 5034, which is herebyincorporated by reference, and is reported in Newtons.

[0033] Hydrostatic Head is a measure of the resistance of a sheet topenetration by liquid water under a static pressure. The test wasconducted according to AATCC-127, which is hereby incorporated byreference, and is reported in centimeters.

[0034] Frazier Air Permeability is a measure of air flow passing througha sheet under a stated pressure differential between the surfaces of thesheet and was conducted according to ASTM D 737, which is herebyincorporated by reference, and is reported in m³/min/m².

[0035] Water Impact is a measure of the resistance of a sheet to thepenetration of water by impact and was conducted according to AATCC42-1989, which is hereby incorporated by reference, and is reported ingrams.

DETAILED DESCRIPTION OF THE INVENTION

[0036] Reference will now be made in detail to the presently preferredembodiments of the invention, examples of which are illustrated below.The present invention is directed to meltblown polyester fibers that arespun from lower viscosity polyesters in order to obtain finer fibers. Asembodied herein, the meltblown fibers are comprised of at least 20% byweight polyester selected from the group consisting of poly(ethyleneterephthalate) having an intrinsic viscosity of less than 0.55 dl/g, andpoly(trimethylene terephthalate) having an intrinsic viscosity of lessthan 0.80 dl/g. The intrinsic viscosity of poly(ethylene terephthalate)polyester that has been meltblown in the past has generally been in therange of 0.65 to 0.80 dl/g. The intrinsic viscosity or “IV” of a polymeris an indicator of the polymer's molecular weight, with a higher IVbeing indicative of a higher molecular weight. Poly(ethyleneterephthalate) with an IV below about 0.55 dl/g is considered to be a“low IV” polyester. Poly(trimethylene terephthalate)(“PTT”) with an IVbelow about 0.80 dl/g is considered to be a “low IV” polyester. The lowIV polyesters useful in the present invention have weight averagemolecular weights of less than 25,000. Preferably, the polyester has aweight average molecular weight in the range of 5,000 to 22,000. Morepreferably, the polyester has a weight average molecular weight in therange of 10,000 to 19,000.

[0037] Low IV polyester has not been used in making meltblown fibers orwebs. It has been found that when low IV polyester is meltblown, thefibers produced have a smaller diameter than fibers meltblown fromconventional IV polyester. These smaller diameter fibers provideimproved barrier properties when used in composite SMS fabrics.

[0038] According to the invention, the fine polyester meltblown fibersof the invention are produced according to a conventional meltblowingprocess. In the meltblowing process, one or more extruders supply meltedpolymer to a die tip where the polymer is fiberized as it passes throughfine capillary openings to form a curtain of filaments. The filamentsare pneumatically drawn and normally broken by a jet of air around thefine capillary openings in the die. The fibers are deposited on a movingbelt or screen, a scrim, or another fibrous layer. Fibers produced bymelt blowing are generally discontinuous fibers having an effectivediameter in the range of about 0.5 to about 10 microns. As used herein,the “effective diameter” of a fiber with an irregular cross section isequal to the diameter of a hypothetical round fiber having the samecross sectional area.

[0039] In order to make thermally bonded meltblown polyester webs thatare more pliable and durable, the meltblown fibers can be spun asmultiple component fibers wherein one of the fiber components iscomprised of low IV polyester. The fibers in the multiple componentmeltblown web of the invention are typically discontinuous fibers havingan average effective diameter of between about 0.5 microns and 10microns, and more preferably between about 1 and 6 microns, and mostpreferably between about 2 and 4 microns. Multiple component meltblownwebs are formed from at least two polymers simultaneously spun from aspin pack. Preferably, the multiple component meltblown web is abicomponent web made from two polymers. The configuration of the fibersin the bicomponent web is preferably a side-by-side arrangement in whichmost of the fibers are made of two side-by-side polymer components thatextend for a significant portion of the length of each fiber.Alternatively, the bicomponent fibers may have a sheath/core arrangementwherein one polymer is surrounded by another polymer, an“islands-in-the-sea” arrangement in which multiple strands of onepolymer are imbedded in another polymer, or any other conventionalbicomponent fiber structure. Without wishing to be bound by theory, itis believed that the attenuation of the meltblown fibers can actuallyfracture the multiple component filaments into even finer filaments,some of which can contain only one polymer component.

[0040] According to the invention, the second polymer component of themultiple component meltblown web comprises one or more fiber formingsynthetic polymers that are more pliable than polyester. Preferably, thesecond component has a melt temperature less than the melt temperatureof the first component so as to help bind the meltblown fibers uponthermal bonding, which results in a more pliable web. Preferably, theother polymer or polymers are gamma radiation stable polymers such aspolyethylene. Alternatively, the second polymer component can be anon-radiation sterilizable polymer such as polypropylene if the end usefor the sheet does not require that the sheet be radiation sterilizable.

[0041] The preferred multiple component meltblown web of the inventionis a bicomponent meltblown web comprised of low IV PET and polyethylene.Preferably, the low IV PET component comprises from 20% to 98% by weightof the meltblown web and the polyethylene component comprises from 2% to80% by weight of the meltblown web. More preferably, the low IV PETcomponent comprises from 55% to 98% by weight of the meltblown web andthe polyethylene component comprises from 2% to 45% by weight of themeltblown web. Even more preferably, the low IV PET component comprisesfrom 65% to 97% by weight of the meltblown web and the polyethylenecomponent comprises from 3% to 35% by weight of the meltblown web. Mostpreferably, the low IV PET component comprises from 80% to 95% by weightof the meltblown web and the polyethylene component comprises from 5% to20% by weight of the meltblown web.

[0042] The fibers of the meltblown web of the invention can be meltblownusing a meltblowing apparatus having capillary die openings like thatshown in FIG. 1 and more fully described in U.S. Pat. No. 4,795,668,which is hereby incorporated by reference. In the sectional view of ameltblowing die 20 shown in FIG. 1, two different polymeric componentsare melted in parallel extruders 23 and 24 and metered separatelythrough gear pumps (not shown) and conduits 25 and 26 into the diecavity 22. In the die cavity, the polymer components form a layered massin which the two components segregate as discrete layers. The layeredmass is extruded through a line of capillary orifices 21. Where singlecomponent fiber is desired, the same polymer is supplied by the twoextruders 23 and 24, or just one extruder is used. A jet of hot airsupplied from the channels 28 attenuates the emerging polymer filaments.Without wishing to be bound by theory, it is believed that the air jetmay fracture the filaments into even finer filaments. The resultingfilaments are believed to include bicomponent filaments in which eachfilament is made of two separate polymer components that both extend thelength of the meltblown fiber in a side-by-side configuration. The finefibers of layer 14 could alternatively be produced by other knowmeltblowing processes, as for example by the process wherein anindividual air nozzle surrounds each polymer capillary, as disclosed inU.S. Pat. No. 4,380,570.

[0043] A composite nonwoven sheet incorporating the meltblown web of theinvention is shown in FIG. 2. The sheet 10 is a three layer compositefabric in which an inner layer 14 is comprised of very fine meltblownpolymer fibers sandwiched between outer layers 12 and 16, which are eachcomprised of larger and stronger and bonded fibers. The very fine fibersof inner layer 14, when formed into the layer 14, produce a barrierlayer with extremely fine passages. The layer 14 acts as a barrier tofluids but does not prevent the passage of moisture vapor. The bondedfiber layers 12 and 16 are comprised of coarser and stronger fibers thatcontribute strength, and in some instances barrier, to the compositesheet. A composite sheet may alternatively be formed as a two layercomposite 18, as shown in FIG. 3. In the two layer composite sheet, thefine meltblown fiber layer 14 is attached on just one side to thecoarser and stronger bonded layer 12. According to alternativeembodiments of the invention, the composite sheet may be made withmultiple layers of fine meltblown fibers like the layer 14, or it may bemade with more than two layers of coarser and stronger fiber layers likethe layers 12 and 16.

[0044] The larger and stronger bonded fibers of the layers 12 and 16 arepreferably conventional meltspun fibers or some other type of strongspunbond fiber. Preferably, the meltspun fibers are substantiallycontinuous fibers. Alternatively, the layers 12 and 16 could be anair-laid or wet-laid staple fiber web or a carded web wherein the fibersare bonded to each other to form a strong web structure. The fibers oflayers 12 and 16 should be made of a polymer to whichpolyethylene-containing fine fibers of the core layer 14 can readilybond. The fibers of layers 12 and 16 are preferably gamma radiationsterilizable in that they have an outer layer comprised of a polymerother than polypropylene, such as polyester, polyethylene, polyamide, orsome combination thereof. Where the composite fabric will not be used inend use applications where radiation sterilization is used, the fibersof layers 12 and 16 could also be comprised of a polymer such aspolypropylene that is not gamma radiation sterilizable.

[0045] A preferred meltspun fiber for the layers 12 and 16 is abicomponent fiber comprised of polyester and polyethylene. The polyestercomponent contributes to the strength to the fabric while thepolyethylene component makes the fabric softer and more drapable. Inaddition, the polyethylene component has a lower melting temperaturethan the polyester component of the fiber so as to make the layers 12and 16 more readily bondable to the fine meltblown fibers of the corelayer 14 using a thermal bonding process. Alternatively, layers 12 and16 could be comprised of a blend of single polymer component fibers, asfor example, a spunbond web wherein a portion of the fibers arepolyethylene fibers and a portion of the fibers are polyester fibers.

[0046] Preferably, the larger and stronger fibers of the layers 12 and16 are substantially continuous spunbonded fibers produced using a highspeed melt spinning process, such as the high speed spinning processesdisclosed in U.S. Pat. Nos. 3,802,817; 5,545,371; and 5,885,909; whichare hereby incorporated by reference. According to the preferred highspeed melt spinning process, one or more extruders supply melted polymerto a spin pack where the polymer is fiberized as it passes throughopenings to form a curtain of filaments. The filaments are partiallycooled in an air quenching zone. The filaments are then pneumaticallydrawn to reduce their size and impart increased strength. The filamentsare deposited on a moving screen, belt, scrim or other fibrous layer.Fibers produced by the preferred high speed melt spinning process aresubstantially continuous and have a diameter of from 5 to 30 microns.These fibers can be produced as single component fibers, as multiplecomponent fibers, or some combination thereof. Multicomponent fibers canbe made in various known cross-sectional configurations, includingside-by-side, sheath-core, segmented pie, or islands-in-the-seaconfigurations.

[0047] A composite nonwoven fabric incorporating the low intrinsicviscosity polyester meltblown web described above can be producedin-line using the apparatus that is shown schematically in FIG. 4.Alternatively, the layers of the composite sheet can be producedindependently and later combined and bonded to form the composite sheet.The apparatus shown in FIG. 4 includes spunbonded web productionsections 80 and 94 well-known in the art. The apparatus of FIG. 4further includes a meltblown web production section 82 incorporating themeltblowing apparatus described with regard to FIG. 1 above. Forpurposes of illustration, the two spunbond web production sections 80and 94 and the meltblown web production section 82 are shown makingbicomponent fibers. It is contemplated that the spunbond web productionsections 80 and 94 and the meltblown web production section 82 could bereplaced by units designed to produce webs having just one polymercomponent or having three or more polymer components. It is alsocontemplated that more than one spunbond web production section could beused in series to produce a web made of a blend of different single ormultiple component fibers. Likewise, it is contemplated that more thanone meltblown web production section could be utilized in series inorder to produce composite sheets with multiple meltblown layers. It isfurther contemplated that the polymer(s) used in the various webproduction sections could be different from each other. Where it isdesired to produced a composite sheet having just one spunbond layer andone fine fiber layer (as shown in FIG. 3), the second spunbond webproduction section 94 can be turned off or eliminated.

[0048] According to the preferred embodiment of the invention, in thespunbond web production sections 80 and 94 of the apparatus shown inFIG. 4, two thermoplastic polymer components A and B are melted,filtered and metered (not shown) to the spin packs 56 and 96. The meltedpolymer filaments 60 and 100 are extruded from the spin packs throughspinneret sets 58 and 98, respectively. The filaments may be extruded asbicomponent filaments having a desired cross section, such as asheath-core filament cross section. Preferably, a lower meltingtemperature polymer is used for the sheath section while a highermelting temperature polymer is used for the core section. The resultingfilaments 60 and 100 are cooled with quenching air 62 and 102. Thefilaments next enter pneumatic draw jets 64 and 104 and are drawn bydrawing air 66 and 106. The fibers 67 from the spunbond web productionsection 80 are deposited onto forming screen 68 so as to form a spunbondlayer 12 on the belt.

[0049] According to the preferred embodiment of the invention, a lowintrinsic viscosity polyester polymer and another polymer are combinedto make a meltblown bicomponent web in the meltblown web productionsection 82. The two polymers C and D are melted, filtered, and thenmetered (not shown) into the spin pack 84. The melted polymers arecombined in the spin pack 84 and exit the spin pack through a line ofcapillary openings 86 like those described above with regard to FIG. 1.Preferably, the spin pack 84 generates the desired side-by-side fiberfilament cross section. Alternative spin pack arrangements can be usedto produce alternative fiber cross sections, such as a sheath-core crosssection. A jet of hot air 88 supplied from the channels 90 impacts onthe opposite side of the exiting filaments 91 and attenuates eachfilament 91 immediately after each filament exits its capillary opening.The meltblown filaments 91 are generally fractured during theattenuation process. The meltblown filament fibers 91 deposit ontospunbond layer 12 to create the multiple component meltblown web layer14.

[0050] Where a second spunbond web production section 94 is used,substantially continuous spunbond fibers 107 from the spunbond webproduction section 80 are deposited onto the meltblown layer 14 so as toform a second spunbond layer 16 of the composite sheet. The layers 12and 16 do not necessarily have to have the same thickness or basisweight.

[0051] The spunbond-meltblown-spunbond web structure is passed betweenthermal bonding rolls 72 and 74 in order to produce the compositenonwoven web 10 which is collected on a roll 78. Preferably, the bondingrolls 72 and 74 are heated rolls maintained at a temperature within plusor minus 20° C. of the lowest melting temperature polymer in thecomposite. For the polyethylene-containing composite sheet of theinvention, a bonding temperature in the range of 115-120° C. and abonding pressure in the range of 350-700 N/cm have been applied toobtain good thermal bonding. Alternative methods for bonding the layersof the composite sheet include calender bonding, through-air bonding,steam bonding, and adhesive bonding.

[0052] Optionally, a fluorochemical coating can be applied to thecomposite nonwoven web to reduce the surface energy of the fiber surfaceand thus increase the fabric's resistance to liquid penetration. Forexample, the fabric may be treated with a topical finish treatment toimprove the liquid barrier and in particular, to improve barrier to lowsurface tension liquids. Many topical finish treatment methods are wellknown in the art and include spray application, roll coating, foamapplication, dip-squeeze application, etc. Typical finish ingredientsinclude ZONYL® fluorochemical (available from DuPont, Wilmington, Del.)or REPEARL® fluorochemical (available from Mitsubishi Int. Corp, NewYork, N.Y.). A topical finishing process can be carried out eitherin-line with the fabric production or in a separate process step.Alternatively, such fluorochemicals could also be spun into the fiber asan additive to the melt.

[0053] The composite nonwoven sheet preferably has a basis weight in therange of 10 to 120 g/m², and more preferably within the range of 30 to90 g/m², and most preferably within the range of 50 to 70 g/m². The grabtensile strength of the composite nonwoven sheet can range widelydepending on the thermal bonding conditions employed. Typical grabtensile sheet strengths (in both the machine and cross directions) arefrom 35 to 400 N, and more preferably from 40 to 300 N, and mostpreferably from 50 to 200 N. The inner meltblown fiber layer of thecomposite sheet typically has a basis weight of between 2 and 40 g/m²,and more preferably between 5 and 30 g/m², and most preferably between12 and 25 g/m². The outer layer of the composite contributes strength,and is some instances barrier, to the composite nonwoven fabric. Each ofthe outer layers typically have a basis weight between 3 and 50 g/m²,and more preferably between 8 and 40 g/m², and most preferably between12 and 35 g/m². Preferably, the layers of the composite sheet aresecured together by thermal bonding, as for example via the melting of alow melting temperature component polymer in the fine fiber layer 14and/or the larger fiber layers 12 and 16. According to the preferredembodiment of the invention, the composite sheet exhibits a hydrostatichead of at least 10 cm, and more preferably of at least 25 cm, and yetmore preferably of at least 45 cm, and most preferably at least 60 cm.It is further preferred that the composite sheet exhibit a water impactof less than 5 g, and more preferably less than 2 g, and most preferablyless than 0.5 g. Finally, it is preferred that the composite sheet has aFrazier Air Permeability greater than 1 m³/min/m², and more preferablygreater than 5 m³/min/m².

[0054] This invention will now be illustrated by the following exampleswhich are intended to illustrate the invention and not to limit theinvention in any manner.

EXAMPLES

[0055] In Example 1 and Comparative Example A, monocomponentpoly(ethylene terephthalate) meltblown fibers were prepared. Thesefibers were meltblown according to the processes described above withreference to the apparatus shown in FIG. 1 with the same polymer beingused in both sides of the bicomponent meltblown spinning apparatus.

[0056] In Example 2 and Comparative Example B, monocomponentpoly(trimethylene terephthalate) meltblown fibers were prepared. Thesefibers were meltblown according to the processes described above withreference to the apparatus shown in FIG. 1 with the same polymer beingused in both sides of the bicomponent meltblown spinning apparatus.

[0057] In Examples 3 and 4, and in Comparative Examples C and D,bicomponent poly(ethylene terephthalate) meltblown fibers were preparedand incorporated into a spunbond-meltblown-spunbond composite sheet. Themeltblown fibers were prepared according to the processes describedabove with reference to the apparatus of FIG. 1 with poly(ethyleneterephthalate) being used on one side and polyethylene/poly(butyleneterephthalate) blend being used on the other side of the bicomponentmeltblown spinning apparatus. A layer of these bicomponent meltblownfibers was sandwiched between spunbond outer layers to make thecomposite sheet like that shown in FIG. 2. The spunbond layers were eachproduced individually using a high speed melt spinning process like thatdescribed above with regard to the spunbond web production section 80 ofthe process shown in FIG. 5. However, instead of preparing all of thelayers in one continuous process as described with reference to FIG. 5,the spunbond layers were each spun, laid down, and rolled up separately.The two spunbond layers and the meltblown layer were subsequentlyunrolled, combined, and thermally bonded to produce thespunbond-meltblown-spunbond composite structure.

Example 1

[0058] Meltblown monocomponent fibers were made with poly(ethyleneterephthalate) available from DuPont as Crystar® polyester (Merge 3949).The poly(ethylene terephthalate) had an intrinsic viscosity of 0.63 dl/gand a weight average molecular weight of 35,600. The poly(ethyleneterephthalate) was used as received without any conditioning or dryingand had a moisture content of about 1300 ppm. The poly(ethyleneterephthalate) polymer was heated to 575° F. (300° C.) in separateextruders. The two polymer components were separately extruded, filteredand metered to a bicomponent spin pack to coalesce into a monocomponentfiber. The die of the spin pack was heated to 600° F. (315° C.). The diehad 601 capillary openings arranged in a 24 inch (61 cm) line. Thepolymer was spun through the each capillary at a polymer throughput rateof 0.80 g/hole/min. Attenuating air was heated to a temperature of 615°F. (323° C.) and supplied at a rate of 225 standard cubic feet perminute (6.4 m³/min) through two 0.8 mm wide air channels. The two airchannels ran the length of the 24 inch line of capillary openings, withone channel on each side of the line of capillaries set back 1 mm fromthe capillary openings. Both streams of poly(ethylene terephthalate)were supplied to the spin pack at a rate of 12 kg/hr. The filaments werecollected on a moving forming screen. As the poly(ethyleneterephthalate) was meltblown, hydrolytic and thermal degradationoccurred which reduced the molecular weight and hence the intrinsicviscosity of the polymer forming the meltblown fibers. The poly(ethyleneterephthalate) in the meltblown fibers had an intrinsic viscosity of0.34 dl/g and a weight average molecular weight of 16,500. The averagefiber diameter is reported in Table 1.

Comparative Example A

[0059] Meltblown monocomponent fibers were formed according to theprocedure of Example 1 except that the poly(ethylene terephthalate) wasdried for 4 hours at 120° C. prior to meltblowing which produced a lowermoisture content of about 50 ppm. The poly(ethylene terephthalate) inthe meltblown fibers had an intrinsic viscosity of 0.59 dl/g and aweight average molecular weight of 31,000. The average fiber diameter isreported in Table 1.

[0060] The undried poly(ethylene terephthalate) with higher moistercontent of Example 1 yielded a lower weight average molecular weight anda lower intrinsic viscosity after spinning than the dried poly(ethyleneterephthalate) with lower moisture content of Comparative Example A. Thepresence of additional water in the higher moisture content examplecontributed to greater polymer chain break up than in the lower moisturecontent example. Table 1 shows that meltblown fibers made of the lowerIV poly(ethylene terephthalate) of Example 1 have a smaller averagefiber diameter than the conventional IV poly(ethylene terephthalate) ofComparative Example A. The lower intrinsic viscosity and weight averagemolecular weight of the poly(ethylene terephthalate) from the fibers ofExample 1 allowed the fibers to be drawn to smaller average fiberdiameters.

Example 2

[0061] Meltblown monocomponent fibers were formed according to theprocedure of Example 1 except that poly(trimethylene terephthalate) wasused in place of the poly(ethylene terephthalate). The poly(trimethyleneterephthalate) resin was had an intrinsic viscosity of 0.70 dl/g. Thepoly(trimethylene terephthalate) was dried for 8 hours at 110° C. Thispolymer was meltblown according to the process of Example 1, except thatthe extruder was heated to about 518° F. (270° C.) and the die of thespin pack was heated to about 518° F. (270° C.). The average fiberdiameter is reported in Table 1.

Comparative Example B

[0062] Meltblown monocomponent fibers were formed according to theprocedure of Example 2 except that the poly(trimethylene terephthalate)resin had a higher intrinsic viscosity of 0.84 dl/g. The average fiberdiameter is reported in Table 1.

[0063] Table 1 shows that meltblown fibers made with the lower intrinsicviscosity poly(trimethylene terephthalate) of Example 2 have a smalleraverage fiber diameter than the fibers produced from the higherintrinsic viscosity poly(trimethylene terephthalate) of ComparativeExample B. TABLE 1 MELTBLOWN FIBER PROPERTIES PET PTT Average IV IVFiber Diameter Example (dl/g) (dl/g) (micron) 1 0.34 3.6 A 0.59 4.9 20.70 2.9 B 0.84 5.5

Example 3

[0064] A meltblown bicomponent web was made with a poly(ethyleneterephthalate) component and a second component comprising apolyethylene/poly(butylene terephthalate) blend. This meltblown web wasincorporated into a spunbond-meltblown-spunbond composite sheet.

[0065] In the meltblown web, the poly(ethylene terephthalate) componentwas Crystar® polyester (Merge 3949), available from DuPont. Thepoly(ethylene terephthalate) had an intrinsic viscosity of 0.63 dl/g anda weight average molecular weight of 35,600. The poly(ethyleneterephthalate) was used as received without any conditioning or dryingand had a moisture content of about 1300 ppm. Thepolyethylene/poly(butylene terephthalate) bicomponent blend contained90% by weight linear low density polyethylene with a melt index of 150g/10 minutes (measured according to ASTM D-1238) available from Dow asASPUN 6831A and 10% by weight poly(butylene terephthalate) availablefrom Hoechst as Merge 1300A. The bicomponent polymer blend was preparedby mixing the polyethylene and poly(butylene terephthalate) in anextruder at 265° C. The poly(ethylene terephthalate) polymer was heatedto 575° F. (300° C.) and the polyethylene/poly(butylene terephthalate)bicomponent polymer blend was heated to 510° F. (265° C.) in separateextruders. The two polymer components were separately extruded, filteredand metered to a bicomponent spin pack arranged to provide aside-by-side filament cross section. The die of the spin pack was heatedto 600° F. (315° C.). The die had 601 capillary openings arranged in a24 inch (61 cm) line. The polymers were spun through each capillary at apolymer throughput rate of 0.80 g/hole/min. Attenuating air was heatedto a temperature of 615° F. (323° C.) and supplied at a rate of 300standard cubic feet per minute (8.5 m³/min) through two 0.8 mm wide airchannels. The two air channels ran the length of the 24 inch line ofcapillary openings, with one channel on each side of the line ofcapillaries set back 1 mm from the capillary openings. The poly(ethyleneterephthalate) was supplied to the spin pack at a rate of 12 kg/hr andthe polyethylene/poly(butylene terephthalate) was supplied to the spinpack at a rate of 12 kg/hr. A bicomponent meltblown web was producedthat was 50 weight percent poly(ethylene terephthalate) and 50 weightpercent polyethylene/poly(butylene terephthalate). The filaments werecollected on a moving forming screen to produce a meltblown web. Themeltblown web was collected on a roll. The meltblown web had a basisweight of 17 g/m².

[0066] As the poly(ethylene terephthalate) was meltblown, hydrolytic andthermal degradation occurred which reduced the molecular weight andhence the intrinsic viscosity of the polymer forming the meltblownfibers. The poly(ethylene terephthalate) in the meltblown fibers had anintrinsic viscosity of 0.34 dl/g and a weight average molecular weightof 16,500.

[0067] The spunbond outer layers were bicomponent fibers with asheath-core cross section. The spunbond fibers were made using anapparatus like that described above with regard to FIG. 4. Spunbond webswith two basis weights (17 g/m² and 24 g/m²) were produced for use inthe outer layers of the composite sheet. The spunbond bicomponent fiberswere made from linear low density polyethylene with a melt index of 27g/10 minutes (measured according to ASTM D-1238) available from Dow asASPUN 6811A, and poly(ethylene terephthalate) polyester with anintrinsic viscosity of 0.63 dl/g and weight average molecular weight ofapproximately 35,6 00 available from DuPont as Crystar® polyester (Merge3949). The polyester resin was crystallized at a temperature of 180° C.and dried at a temperature of 120° C. to a moisture content of less than50 ppm before use.

[0068] The poly(ethylene terephthalate) used in the spunbond layers washeated to 290° C. and the polyethylene was heated to 280° C. in separateextruders. The polymers were extruded, filtered and metered to abicomponent spin pack maintained at 295° C. and designed to provide asheath-core filament cross section. The polymers were spun through thespinneret to produce bicomponent filaments with a polyethylene sheathand a poly(ethylene terephthalate) core. The total polymer throughputper spin pack capillary was 1.0 g/min for the 17 g/m² basis weight weband 1.0 g/min for the 24 g/m² web. The polymers were metered to providefilament fibers that were 30% polyethylene (sheath) and 70% polyester(core), based on fiber weight. The resulting smaller, strongersubstantially continuous filaments were deposited onto a laydown beltwith vacuum suction. The fibers in the two webs (17 g/m² and 24 g/m²basis weights) had an effective diameter in the range of 9 to 12microns. The resulting webs were separately passed between two thermalbonding rolls to lightly tack the web together for transport using apoint bonding pattern at a temperature of 100° C. and a nip pressure of100 N/cm. The line speed during bonding was 206 m/min for the 17 g/m²basis weight web and 146 m/min for the 24 g/m² basis weight web. Thelightly bonded spunbond webs were each collected on a roll.

[0069] The composite nonwoven sheet was prepared by unrolling the 17g/m² basis weight spunbond web onto a moving belt. The meltblownbicomponent web was unrolled and laid on top of the moving spunbond web.The second roll of the 24 g/m² basis weight spunbond web was unrolledand laid on top of the spunbond-meltblown web to produce aspunbond-meltblown-spunbond composite nonwoven web. The composite webwas thermally bonded between an engraved oil-heated metal calender rolland a smooth oil heated metal calender roll. Both rolls had a diameterof 466 mm. The engraved roll had a chrome coated non-hardened steelsurface with a diamond pattern having a point size of 0.466 mm², a pointdepth of 0.86 mm, a point spacing of 1.2 mm, and a bond area of 14.6%.The smooth roll had a hardened steel surface. The composite web wasbonded at a temperature of 110° C., a nip pressure of 350 N/cm, and aline speed of 20 m/min. The bonded composite sheet was collected on aroll. The final basis weight of this composite nonwoven sheet was 58g/m². The physical properties of the sheet are reported in Table 2.

Comparative Example C

[0070] A composite sheet was formed according to the procedure ofExample 3 except that the poly(ethylene terephthalate) was dried for 4hours at 120° C. prior to meltblowing which produced a lower moisturecontent of about 50 ppm. The intrinsic viscosity of the poly(ethyleneterephthalate) polymer in the meltblown fibers was 0.59 dl/g and theweight average molecular weight was 31,000. The physical properties ofthe composite sheet are reported in Table 2.

[0071] Table 2 shows that a composite sheet made with meltblown fibersmade of the lower viscosity poly(ethylene terephthalate) of Example 3exhibits increased hydrostatic head as compared to the composite sheetof Comparative Example C.

Example 4

[0072] A composite sheet was formed according to the procedure ofExample 3 except that the air flow rate during the melt blowing processwas 310 standard cubic feet per minute (8.8 m³/min) instead of 300standard cubic feet per minute (8.5 m³/min). The physical properties ofthe sheet are reported in Table 2.

Comparative Example D

[0073] A composite sheet was formed according to the procedure ofComparative Example C except that the air flow rate during the meltblowing process was 500 standard cubic feet per minute (14.1 m³/min)instead of 300 standard cubic feet per minute (8.5 m³/min). The physicalproperties of the sheet are reported in Table 2.

[0074] Table 2 shows a composite sheet made with meltblown fibers madeof the lower viscosity poly(ethylene terephthalate) of Example 4exhibits increased hydrostatic head as compared to the composite sheetof Comparative Example D. TABLE 2 NONWOVEN WEB PROPERTIES Hydro- GrabGrab Meltblown static Frazier⁺ Tensile Tensile PET IV Meltblown Head(m³/ MD XD Example (dl/g) PET Mw (cm) min/m²) (N) (N) 3 0.34 16,500 7727 143.4 77.5 C 0.59 31,000 40 65 139.8 86.0 4 0.34 16,500 83 28 140.281.5 D 0.59 31,000 58 39 147.8 77.5

What is claimed is:
 1. A meltblown fiber comprising at least 20% byweight polyester selected from the group consisting of poly(ethyleneterephthalate) having an intrinsic viscosity of less than 0.55 dl/g, andpoly(trimethylene terephthalate) having an intrinsic viscosity of lessthan 0.80 dl/g.
 2. The meltblown fiber of claim 1 wherein the fiber hasan average effective diameter of less than 10 microns, and wherein theintrinsic viscosity of the poly(ethylene terephthalate) is in the rangeof 0.20 to 0.50 dl/g and the intrinsic viscosity of thepoly(trimethylene terephthalate) is in the range of 0.45 to 0.75 dl/g.3. The meltblown fiber of claim 2 wherein the intrinsic viscosity of thepoly(ethylene terephthalate) is in the range of 0.25 to 0.45 dl/g andthe intrinsic viscosity of the poly(trimethylene terephthalate) is inthe range of 0.50 to 0.70 dl/g.
 4. The meltblown fiber of claim 1wherein said fiber is a multiple component fiber comprised of between20% and 98% by weight of poly(ethylene terephthalate) and between 80%and 2% by weight of a second polymer component.
 5. The meltblown fiberof claim 4 wherein said second polymer component comprises of at least10% of polyethylene polymer.
 6. A web of meltblown fibers, said webcomprised of at least 20% by weight polyester selected from the groupconsisting of poly(ethylene terephthalate) having an intrinsic viscosityof less than 0.55 dl/g, and poly(trimethylene terephthalate) having anintrinsic viscosity of less than 0.80 dl/g.
 7. The web of claim 6 thefibers of the web have an average effective diameter of less than 10microns, and wherein the intrinsic viscosity of the poly(ethyleneterephthalate) is in the range of 0.20 to 0.50 dl/g and the intrinsicviscosity of the poly(trimethylene terephthalate) is in the range of0.45 to 0.75 dl/g.
 8. The web of claim 7 wherein the intrinsic viscosityof the poly(ethylene terephthalate) is in the range of 0.25 to 0.45 dl/gand the intrinsic viscosity of the poly(trimethylene terephthalate) isin the range of 0.50 to 0.70 dl/g.
 9. The web of claim 6 wherein the webis comprised of multiple component fibers and the web is comprised ofbetween 20% and 98% by weight of poly(ethylene terephthalate) andbetween 80% and 2% by weight of a second polymer component.
 10. The webof claim 9 wherein said second polymer component comprises at least 10%by weight of polyethylene polymer.
 11. A composite sheet comprising: afirst fibrous layer having a first side and an opposite second side; asecond fibrous layer bonded to said first side of said first fibrouslayer; said first fibrous layer being a meltblown web comprised of atleast 20% by weight polyester selected from the group consisting ofpoly(ethylene terephthalate) having an intrinsic viscosity of less than0.55 dl/g, and poly(trimethylene terephthalate) having an intrinsicviscosity of less than 0.80 dl/g; said second fibrous layer comprised ofat least 95% by weight of meltspun fibers; said composite sheet having abasis weight of less than 120 g/m², and a hydrostatic head of at least10 cm.
 12. The composite sheet of claim 11 wherein at least 10% of themeltblown fibers in said first fibrous layer are multiple componentfibers having a length, said multiple component fibers having first andsecond polymer components arranged in a manner such that said first andsecond polymer components each extend substantially the complete lengthof said bicomponent fibers.
 13. The composite sheet of claim 12 whereinsaid first and second polymer components of said bicomponent meltblownfibers are arranged in a side-by-side arrangement.
 14. The compositesheet of claim 12 wherein said first polymer component comprises between20% and 98% by weight of said first fibrous layer and said secondpolymer component comprises between 80% and 2% of said first fibrouslayer, and said second polymer component of said first fibrous layerconsists essentially of polyethylene.
 15. The composite sheet of claim14 wherein the meltspun fibers of said second fibrous layer are multiplecomponent fibers having a polyester component and a polyethylenecomponent, wherein the polyester component comprises at least 10% byweight of the second fibrous layer and the polyethylene componentcomprises at least 10% by weight of the second fibrous layer.
 16. Agarment comprised of the composite sheet of claim
 11. 17. A meltblownfiber comprising at least 20% by weight polyester having a weightaverage molecular weight of less than 25,000.
 18. The meltblown fiber ofclaim 17 wherein said polyester has a weight average molecular weight inthe range of 5,000 to 22,000.
 19. The meltblown fiber of claim 18wherein said polyester has a weight average molecular weight in therange of 10,000 to 19,000.
 20. The meltblown fiber of claim 17 whereinsaid polyester is poly(ethylene terephthalate).